This invention relates to apparatus for recording the opening or closing or a closure member.
More particularly, the invention relates to apparatus for recording the opening or closing of a closure member such as a door controlling access to an enclosed space. The invention is particularly, though not exclusively, concerned with goods vehicles such as closed lorries or vans.
When goods vehicles are loaded they are usually sealed at the point of dispatch by means of a metal or wire seal which passes through the door or shutter catch. Each seal has stamped on it a unique number which is recorded on the driver's delivery documents. At the point of delivery the number on the seal is compared with that on the documents to check whether the vehicle has been opened. This system has a number of disadvantages. Some mechanical seals can be "locked" to appear sealed when in fact they are not. The seals can only be used once, and so add to the expense of vehicle operation. Moreover, to have numerous stocks of seals at all the locations a vehicle may visit is costly and reduces the security of the system as the allocation of the seals must be carefully controlled.
U.S. Pat. No. 4,118,047 describes a reusable seal consisting of a body and a wire loop, the ends of which pass through holes in the body and are clamped in position by plungers actuated by turning a drum rotatably mounted in the body. One side of the drum forms a tray containing a large number of balls of different colours, and rotating the drum to the clamping position moves five of the balls into a recess in the body, in which they are visible from outside the body. The five visible balls provide a colour code which is changed if the drum is rotated to release and unclamp the wire loop, so giving an indication that the seal has been tampered with. This provides a reusable seal, but requires a complex mechanism.
It is an object of this invention to provide apparatus which can be used instead of mechanical seals, and which can be manufactured simply and inexpensively.